In the field of petroleum production, various techniques may be employed for raising viscous fluids, such as crude oil to the earth's surface from a wellbore. In a typical well, perforations are formed in the casing of a wellbore through which production fluids, such as crude oil, may penetrate and collect in the wellbore. Where ambient pressures are insufficient to force the fluid to the earth's surface for processing, submergible pumps are typically employed to pump production fluids up through the wellbore to collection points. Such wells and pumping arrangements may be located both on dry land and beneath bodies of water, such as over continental shelves, lakes, swamps and the like.
Known submergible pumping systems for petroleum wells typically include a pump coupled to a submergible electric motor. A motor protector may be provided adjacent to the electric motor to protect against temperature and pressure variations in the portion of the wellbore where the submergible unit will be positioned. Inlet apertures surrounding the pump allow production fluids to flow into the pump. The electric motor drives the pump in rotation to pressurize the production fluids and to force them through a conduit to the earth's surface. Pumping units generally of this type are commercially available from Reda of Bartlesville, Okla.
While heretofore known pumping systems are generally sufficient to collect and pump many production fluids from wellbores, they may experience difficulties in handling particularly viscous or heavy fluids. Because the viscosity of such fluids is generally a function of temperature, in certain applications heaters have been employed adjacent to submergible pumping units to preheat the fluids until their viscosity becomes sufficiently low to be pumped from the wellbore. In extreme cases, such heaters may be employed to melt solidified petroleum, paraffin waxes, hydrates and the like which can, once liquefied, be pumped via the submergible pumping system to the earth's surface.
Submergible heating systems of the type mentioned above are commonly attached to existing pumping systems including electric motor and pump sets. The heating system is powered by electrical energy transmitted through independent cables which run adjacent to the pumping system and upward through the wellbore to a power supply located at the earth's surface. Control of the heating unit is accomplished by modulating power input to the heating unit through the power supply cables. Because the heating unit is powered independently of the pumping unit, the heating unit cables are in addition to the power supply and control cables used to provide electrical energy for driving the electric motor.
While such arrangements may, in certain applications, provide adequate heating for viscous wellbore fluids, they are not without drawbacks. For example, depending upon the relative sizes of the wellbore casing and of the electric motor and pump assembly, very little clearance may be available in the wellbore for the additional power cables necessary to supply electrical energy to the heater. Similarly, the provision of multiple power cables for the heating unit and the pumping unit add considerable cost and weight to the pumping system. Furthermore, such arrangements typically require separate power supplies and associated controls for the heating unit and the submergible electric motor. All of these factors contribute to significantly increasing the overall cost of the submergible pumping system and render the equipment more difficult to assemble, install and manage.
There is a need, therefore, for an improved technique for heating viscous fluids in a well which addresses these drawbacks of existing systems. In particular, there is a need for a submergible pumping system which can, in addition to pumping, reduce the viscosity of the viscous fluids adjacent to the pumping unit by heating these viscous fluids and thereby improve the ability of the submergible pumping system to pump and which does not require the addition of heater elements to the submergible pumping system.